506 SEVENTH REPORT—1837. 
The following were the plants introduced into these vessels : 
In glass 1 were Sedum rupestre and telephium, Veronica 
repens, Gentiana acaulis, Erigeron hellidifolius, Lobelia 
fulgens, Saxifraga virginiana and irrigua. 
In glass 2 were Primula vulgaris, Anemone nemorosa, 
Pulmonaria angustifolia, Alchemilla vulgaris, Valeriana 
dioica, Veronica repens, Lobelia fulgens. 
In glass 3 were Primula veris and auricula, Erigeron helli- 
difolius, Dianthus armeria, Sempervivum montanum, and 
Lobelia fulgens. 
Now these plants were allowed to remain till May 5th, a 
period of almost 10 days, undisturbed, at the end of which time 
they appeared healthy and had grown considerably ; some even 
had flowered since their introduction. 
The air contained in each jar was then examined during the 
day, a portion of it having been drawn off into an exhausted 
tube through a stop-cock connected with the jar. 
In this manner it was ascertained that the air in jar 1 con- 
tained 4 per cent. of oxygen more than the proportion present 
in atmospheric air; in jar 2, 13} per cent. more; in jar 3, 2 per 
cent. more. 
At night, on the contrary, this excess of oxygen had disap- 
peared, the air examined three hours after sunset corresponding 
in every case as nearly as possible with that present in the at- 
mosphere. 
The following day (May 6th) the results were not equally fa- 
vourable, yet even then in jar 1 there was an excess of 2 per cent. 
of oxygen ; in jar 2 an excess of 1 per cent.; in jar 3 of 2 per 
cent., and this excess was plainly attributable to the action of 
light, for it in a great measure disappeared when the jars were 
left in the dark for a few hours, No. 1 under this treatment 
being found to contain just the quantity present in the atmo- 
sphere, and No. 2 only 0°75 more. 
It would seem then that for a certain period plants have the 
power of thriving and adding to the amount of oxygen, even 
under the circumstances detailed; but that there is a limit to 
this power appeared on a re-examination of the air three weeks 
afterwards (viz., on May 25th), when it was found that jar 1 
contained only 1 per cent. more oxygen than that in the atmo- 
sphere instead of 4, as on the 5th instant, and that jars 2 and 3 
even contained a portion less. 
Examined again on June 20th, No. 1 was found to contain 
21 per cent. less of oxygen than that in atmospheric air; 
No. 2, 33 less; No, 3, 4 per cent. less. We seem therefore 
